Water Fall Model :

If we see the actual model of the water
fall model in figure, because of the cascade from one phase to another this
model is known as the water fall model of software life cycle or linear
sequential model.

As the figure shows, the process is
structured as a cascade of phases, where the output of one phase constitutes
the input of the next one.Each phase,
in turn, is structured as set of activities that might be executed by different
people concurrently.

Figure :Waterfall Model

The phases in the figure are as follows :

Feasibility study.

Requirements analysis and specification.

Design and specification.

Coding and Module testing.

Integration and system testing.

Delivery.

Maintenance.

Feasibility Study :The first phase is known as feasibility study.The purpose of this phase is to produce a
feasibility study document that evaluates the costs and benefits of the
proposed application.

To do so, it is
first necessary to analyze the problem, at least at a global level.The feasibility study is usually done within
limited time bounds and under pressure.

In sum, the
feasibility study tries to anticipate future scenarios of software
development.Its result is a document
that should contain at least following items:

Requirement Analysis
and Specification :This phase exactly tells the requirement and
needs of the project.This is very
important and critical phase in waterfall model.The purpose of a requirements analysis is to
identify the qualities required of the application, in terms of functionality, performance,
ease of use, portability, and so on.

The requirements
describes the “what” of a system, not the “how”.This phase produces a large document,
contains a description of what the system will do without describing how it
will be done.The resultant document is
known as software Requirement Specification (SRS) document.

An SRS document must contain following:

Detailed statement of problem

Possible alternative solution to problem

Functional requirement of the software system

Constraints on the software system

Design and
Specification:The goal of the design phase is to transform
the requirements in the SRS document into a structure that is suitable for
implementation in some programming language.

Two distinctly
different design approaches are available: the traditional design approach and
the object-oriented approach.

Coding and Module
Testing:Coding and module testing is the phase in
which we actually write programs using a programming language.It was the only recognized development phase
in early development processes, but it is just one of several phases in a
waterfall process.The output of this
phase is an implemented and tested collection of modules.

Module testing is
the main quality control activity that is carried out in this phase.Other such activities may include code
inspections to check adherence to coding standards and, more generally, to
check for a disciplined programming style, as well as checking of software
generally, to check for a disciplined programming style, as well as checking of
software qualities other than functional correctness, performance although this
is often better done at a later stage of coding.

Integration and System
Testing:During the integration and system testing
phase, the modules are integrated in a planned manner.The different modules making up a software
product are almost never integrated in one shot.Integration is normally carried out
incrementally over a number of steps.

The objective of
system testing is to determine whether the software system performs as per the requirements
mentioned in SRS documents.This testing
is known as system testing.A fully
developed software product is system tested.The system testing is done in three phases called Alpha, Beta and
Acceptance Testing.

Delivery and
Maintenance: The delivery of software is often done in
two stages.In the first stage, the
application is distributed among a selected group of customers prior to its
official release.The purpose of this
procedure is to perform a kind of controlled experiment to determine, on the
basis of feedback from users, whether any changes are necessary prior to the
official release.In the second stage,
the product is distributed to the customers.

We defined
maintenance as the set of activities that are performed after the system is
delivered to the customer.Basically,
maintenance consists of correcting any remaining errors in the systems
(corrective maintenance), adapting the application to changes in the
environment (adaptive maintenance), and improving changing, or adding features
and qualities to the applications (perfective maintenance).

Merits of Waterfall Model:

1 It is a linear model.

2 It is segmental model.

3 It is systematic and sequential.

4 It is simple one.

5 It has proper documentations.

Demerits of Waterfall
Model:

1 It is difficult to define all requirements at the beginning
of a project.

2 This model is not suitable for accommodating any change.

3 A working version of the system is not seen until late in
the project’s life.

4 It does not scale up well to large project.

5 It involves heavy documentation.

6 We cannot go in the backward direction while SDLC performs.

7 There is no sample model for clearly in realization the customers’
needs.

8 There is no risk analysis.

9 If there is any mistake or error in any phase then we
cannot make good software.

10 It is a document driven process that requires formal documents
at the end of the each phase.